Push switch sealed against contaminants

ABSTRACT

A push switch having a mount base 11 made of a heat resisting and insulating material and having a recess 11a in the top surface thereof, the recess 11a receiving a plurality of contact terminals 12a, 13a disposed such that contact portions constituting at least a pair of conductor circuits are arranged in the recess, a curved push spring 14 having an inverting function and disposed in the recess 11a, and an operating portion through which the push spring 14 is operated so as to turn the switch on and off. A flexible heat resistant film 15 constituting the operating portion is attached to the mount base in a manner such as to cover the entire area of opening of the recess. With this dust proof and semi-hermetic arrangement, it is possible to prevent invasion by dusts and other foreign matters which are strictly to be kept away from the switch. The invasion by flux and molten solder also is avoided so that the switch can be manufactured by new methods such as solder dipping.

TECHNICAL FIELD

The present invention relates to a push switch which is widely used inkeyboards and other inputting manipulation means such as those in videotape recorders, particularly of the type having a mount base made of aheat resisting and insulating material and having a recess in the topsurface thereof, the recess receiving a plurality of contact terminalsdisposed such that contact portions constituting at least a pair ofconductor circuits are arranged in the recess, a curved push springhaving an inverting function and disposed in the recess, and anoperating portion through which the push spring is operated.

PRIOR ART

FIG. 1 shows the construction of a known push switch of the typementioned above.

Referring to this Figure, a mount base 1 has a circular recess 1a formedin the top side thereof. Contact terminals 2a, 3a constituting aconductive circuit are fixed by insertion molding such that the contactportions of these contact terminals are disposed on the bottom surfaceof the recess. These contact terminals 2a and 3a are extended to theoutside of the mount base 1, so as to form external terminals 2b, 3b. Areference numeral 4 denotes a disc-shaped push spring having aninverting function and curved to convex upwardly. The push spring 4 isso shaped that it always contacts with the contact terminals 2a but isnormally kept away from the contact terminal 3a. A reference numeral 5designates a circular push plate which has a projection 5a projectingfrom the central portion of the lower surface thereof, so as to lightlypress the upper surface of the push spring thereby preventing any playof the push spring 4. On the other hand, a projection 5b is formed onthe upper side of the push plate so as to be depressed by a finger whenthe switch is operated. The push plate 5 is received in the recess 1a inthe mount base 1 with a slight play so that it can be moved downwardagainst the force of the push spring 4 when pushed. The push plate 5 isheld by a cover plate 6 fixed to the mount base by means of caulkingtabs 1b provided on the mount base 1. In the normal state of the switch,the push spring contacts only the contact terminals 2a so that theswitch is in OFF state. As the push plate 5 is pressed against thebiasing force of the push spring 4, the push spring contacts also thecontact terminal 3a, whereby the switch is turned on. However, theswitch is turned off again as the push plate 5 is released from thepressing force.

In loading this switch on a printed circuit board by soldering, it isnecessary to dip the terminals 2b and 3b in a soldering flux solution.It is often experienced that, when the height of the push switch issmall, the flux comes into the switch through a minute gap between thecover plate 6 and the push plate 5, partly because of a capillary actionand partly because of flying of the flux particles. It is alsoexperienced that the dust and other foreign matters, as well as thechips of the ground push plate 5, come into the switch so as to cause abad contact in the switch.

On the other hand, there is an increasing demand for a reduction in thesize and thickness of the switch, which in turn has given rise to thedemand for development of a new push switch which can be loaded byre-flow soldering or solder dipping. The conventional push switch,however, cannot meet such a demand.

SUMMARY OF THE INVENTION

According to the invention, there is provided a push switch having amount base made of a heat resisting and insulating material and having arecess in the top surface thereof, the recess receiving a plurality ofcontact terminals disposed such that contact portions constituting atleast a pair of conductor circuits are arranged in the recess, a curvedpush spring having an inverting function and disposed in the recess, andan operating portion through which the push spring is operated so as toturn the switch on and off, the operating portion being constituted by aflexible heat resistant film attached to the mount base in a manner suchas to cover the entire area of opening of the recess.

It is, therefore, possible to obtain a dust-proof and semi-hermeticswitch assembly without complicating the construction, therebyeffectively preventing invasion, into the switch, of dust and otherforeign matters which have to be strictly kept out of the switch. Theuse of the heat resistant film also prevents the flux and molten solderfrom coming into the switch, so that the push switch can be produced bythe new loading technic such as solder dipping or re-flow typesoldering.

BRIEF DESCRIPIION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional push switch;

FIG. 2 is a sectional view of a push switch in accordance with a firstembodiment of the invention;

FIG. 3 is a sectional view of a modification of the push switch of thefirst embodiment;

FIG. 4 is a sectional view of a part which is obtained by fastening apush button to the heat resistant film in the first embodiment;

FIG. 5 is a sectional view of a push switch of another modification ofthe first embodiment, incorporating the part shown in FIG. 4;

FIG. 6 is a sectional view of a second embodiment of the push switch inaccordance with the invention;

FIG. 7 is a sectional view of a second embodiment of the invention;

FIG. 8 is a sectional view of a modification of the second embodiment;

FIG. 9 is a sectional view of the push switch shown in FIG. 8 as viewedfrom the upper side thereof;

FIG. 10 is a sectional view of a third embodiment of the push switch inaccordance with the invention;

FIGS. 11 and 12 are sectional views of a third embodiment of theinvention; and

FIG. 13 is a perspective view of the push switch shown in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 2 shows the construction of a known push switch of the typementioned above.

Referring to this Figure, a mount base 11 has a circular recess 11aformed in the top side thereof. Contact terminals 12a, 13a constitutinga conductive circuit are fixed by insertion molding such that thecontact portions of these contact terminals are disposed on the bottomsurface of the recess. These contact terminals 12a and 13a are extendedto the outside of the mount base 11, so as to form external terminals12b, 13b. A reference numeral 14 denotes a disc-shaped push springhaving an inverting function and curved to convex upwardly. The pushspring 14 is so shaped that it always contacts with the contactterminals 12a but is normally kept away from the contact terminal 13a. Areference numeral 15 denotes a flexible heat resistant film which ismade of, for example, polyimide film. The heat resistant film 15 isadhered to the upper side of the mount base 11 in a manner such as tocover the entire area of the opening of the recess 11a. The heatresistant film 15 is contacted at the central portion of the lowersurface thereof by the central portion of the push spring 14, wherebythe push spring 14 is retained within the recess 11a of the mount base11.

In the normal state of use, the push spring 14 makes contact only withthe contact terminals 12a so that the switch is in OFF state. However,as the heat resistant film 15 is lightly pressed against the biasingforce of the push spring 14, the push spring 14 contacts also with thecontact terminal 13a, whereby the switch is turned on. However, as theheat resistant film is released from the biasing force, the switch isturned off again.

FIG. 3 is a sectional view of a modification of the embodiment shown inFIG. 2. In this embodiment, a heat resistant film 16 which extends tocover both sides of the mount base 11 is used in place of the film 15 inthe first embodiment. Thus, the heat resistant film 16 is adhered notonly to the upper surface of the mount base 11 but also to both sidesurfaces of the same, thereby improving the strength of bonding betweenthe film 16 and the mount base 11. A pressing portion 17 contacting thepush spring 14 and made of a metal such as bronze is fixed to the centerof the lower side of the heat resistant film 16 by, for example,bonding, thereby improving the operation characteristics. For attaininga higher stability, the pressing portion 17 is preferably made of ametal, although it may be made of a resin.

In another modification shown in FIG. 4, a heat resistant film 18 havinga central bore 18a is used in place of the heat resistant film 15 of thefirst embodiment, and a push button 19 having a pressing portion 19a anda button portion 19b and made of a heat resistant resin is integratedwith the heat resistant film 18 by outserting method such that thepressing portion 19a and the button portion 19b project from the lowerside and upper side of the heat resistant film 18, respectively. FIG. 5shows a push switch which exhibits superior stability and operationcharacteristics when operated, by virtue of the use of the arrangementshown in FIG. 4.

FIG. 6 shows a push switch in accordance with a second embodiment of theinvention. This embodiment also incorporates a heat resistant film 16adhered not only to the upper surface but also to the side surface ofthe mount base 11 by a bond. In order to ensure a high strength ofbonding of the heat resistant film 16 to the mount base 11, a heatshrinkable tube 20 is provided on the side surface of the mount base 11,with the heat resistant film 16 sandwiched therebetween. In addition, atleast one minute air vent hole 21 is provided in the side wall of themount base 11, so as to permit the air to pass therethrough in responseto the pressure change in the switch, thereby preventing reduction inthe reliability due to change in the heat condition.

FIG. 7 shows a modification in which a pressing portion 17 is providedas in the case of the embodiment shown in FIG. 3.

FIGS. 8 and 9 show still another modification of the embodiment shown inFIG. 6. This modification has the heat resistant film 18 and the pushbutton 19 of the same type as those shown in FIG. 5.

FIG. 10 shows a third embodiment of the push switch of the invention. Inthis embodiment, a cover 22 made of a conductive metal which isconsidered as being not solderable, e.g., aluminum or a stainless steel,is provided on the heat resistant film 15 which in turn is fixed to theupper surface of the mounting base 11. This cover 22 is provided with acentral circular hole 22a through which the finger can have access tothe central portion of the heat resistant film 15 so as to manipulatethe latter. The cover 22 is fixed to the mount base 11 by caulking, withthe heat resistant film 15 sandwiched therebetween.

FIG. 11 shows a modification of the embodiment shown in FIG. 10. Thismodification has a pressing portion 17 similar to those shown in FIGS. 3and 7. In addition, the cover 22 has an extension 22b which is coatedwith a coating layer 23 of a solderable conductive metal. The coatinglayer 23 serves as a grounding terminal which grounds the cover 22thereby eliminating electrostatic noise.

FIGS. 12 and 13 show another modification of the embodiment shown inFIG. 10. This modification has the heat resistant film 18 and the button19 with the pressing portion 19a and the button portion 19b which aresimilar to those shown in FIGS. 5 and 8. The button portion 19b projectsabove the cover 22 through the central hole 22a. In FIG. 13, a referencenumeral 22c designates a caulking portion by which the cover 22 is fixedto the mounting base 11.

In the push switches of the embodiment shown in FIGS. 10 to 13, thecover 22 made of a conductive metal which can hardly be soldered andcovering the heat resistant film 15, 18 minimizes the risk of breakageof the heat resistant film 15 or 18 by a member having a keen edge, aswell as the risk of separation of the heat resistant film, which mayoccur when the heat resistant film 15 or 18 is exposed. In addition,solderable extension of the cover 22 provides a grounding function.

In the described embodiments, the contact terminals are shown to extendin the horizontal direction and illustrated only in cross-section, itwill be clear that the invention can be effectively applied regardlessof the outer configuration of the push switch, e.g., round or polygonal.It will be understood also that the number of the conductor circuitsconstituted by the contact terminals is not limited to two, although thedescribed embodiments incorporate a pair of conductor circuits.

INDUSTRIAL APPLICABILITY

As has been described, according to the invention, it is possible toobtain a push switch having a dust-proof and semi-hermetic construction,without causing any complication of the construction, whereby dust andother foreign matters, which are strictly to be kept away from theswitch, are prevented from coming into the switch, thereby minimizingthe risk of bad contact in the switch attributable to the invasion bydust and foreign matters. In addition, since the use of the heatresistant film eliminates the possibility of invasion by flux and moltensolder it becomes possible to adopt new loading technic such as solderdipping and re-flowing, thus coping with the demand in the field ofindustry concerned. Furthermore, the necessity for the caulking tabs,which heretofore have been necessary in the conventional switch, iseliminated. It is to be understood also that the size of the push switchcan be minimized without impairing the reliability, by virtue of the useof the flexible thin film on the upper side of the push switch, thuscomplying with the demand for reduction in the weight, thickness andsize of the switch. When a cover of a member made of a conductive metalto which the solder can hardly be deposited is provided to cover theheat resistant film, the risk of damaging of the heat resistant film bystubbing, as well as the risk of separation of the heat resistant filmwhich is liable to occur when the film is uncovered, is minimized.Furthermore, a grounding function is attained by allowing soldering onone end of the cover. At least one air vent hole provided in the sidewall of the mount base permits air to pass therethrough in response to achange in the internal pressure of the switch, thereby avoiding anyunfavorable effect of change in the heat condition on the reliability ofthe push switch.

We claim:
 1. A push switch comprising a mount base made of a heatresisting and insulating material and having a recess in a top surfacethereof, which defines a recess opening, said recess having a pluralityof contact terminals disposed therein, external terminals connected tosaid contact terminals and having planar surface portions which areadapted to be in surface contact with a planar electrode pattern on acircuit board, a curved push spring having an inverting function anddisposed in said recess, and an operating portion through which saidpush spring is operated, said operating portion being formed by aflexible heat resistant film which is hermetically attached to saidmount base to cover the entirety of said recess opening; and a covermade of a material substantially resistant to solder deposition, saidcover covering the entire area of said heat resistant film except thecentral portion of said film.
 2. A push switch according to claim 1,further comprising a pressing portion provided on the lower surface ofsaid heat resistant film to contact said push spring, said pressingportion being made of a metal or a plastic.
 3. A push switch accordingto claim 1, wherein a button is integrated with said heat resistantfilm, said button having a button portion projecting above an uppersurface of said heat resistant film and a pressing portion projectingbelow a lower surface of said heat resistant film so as to contact saidpush spring, said button portion and said pressing portion being made ofplastic material, said button portion projecting above said cover.
 4. Apush switch according to claim 1, wherein said cover has an extensionwhich is coated by a coating layer made of a solderable conductivemetal.
 5. A push switch comprising a mount base made of a heat resistingand insulating material and having a recess in a top surface thereof,which defines a recess opening, said recess having a plurality ofcontact terminals disposed therein, external terminals connected to saidcontact terminals and having planar surface portions which are adaptedto be in surface contact with a planar electrode pattern on a circuitboard, a curved push spring having an inverting function and disposed insaid recess, an operating portion through which said push spring isoperated, said operating portion being formed by a flexible heatresistant film which is hermetically attached to said mount base tocover the entirety of said recess opening, and a cover made of ametallic material substantially resistant to solder deposition, saidcover covering the entire area of said heat resistant film except thecentral portion of said film.